root microbial interaction for crop improvement

2. 2
SEMINAR- I
Rathod Balaji Ulhas
PGS16AGR7165
Department of Biotechnology
Understanding Root -Microbial
interaction for crop improvement
Undstanding root microbial interaction for crop improvement12/05/2017

3. Contents
• INTRODUCTION.
• PLANT-PLANT INTERACTIONS MEDIATED BY ROOT EXUDATES.
 Negative Plant-Plant Interactions
 Positive Plant-Plant Interactions
 Mechanisms That Influence Soil Resources
• PLANT-MICROBE INTERACTIONS MEDIATED BY ROOT
EXUDATES .
 Positive Plant-Microbe Interactions
 Negative Plant-Microbe Interactions
 Case study
 CONCLUSION

5. The functions of the plant root system include
 Anchorage and support
 Absorption and conduction
 Storage
 Photosynthesis
 Movement
No plant can live or grow without
roots. Hence, roots are very
important

6. Why is soil important?
 Microorganisms in soil are important because they
affect soil structure and fertility. Soil microorganisms can be
classified as bacteria, actinomycetes, fungi, algae and
protozoa. Each of these groups has characteristics that define
them and their functions in soil.

7. The Role of Root Exudates in Rhizosphere Interactions with
Plants and Other Organisms
 . Plant roots exude an enormous range of potentially valuable
small molecular weight compounds into the rhizosphere.
 Root exudation includes the secretion of ions, free oxygen and
water, enzymes, mucilage, and a diverse array of carbon
containing primary and secondary metabolites

9. Types of intractions
 Interactions involving plants roots in the rhizosphere include
root-root interactions
root-insect, and
root-microbe interactions
 interactions may be classified as either positive or negative
associations

12. PLANT-PLANT INTERACTIONS MEDIATED BY ROOT
EXUDATES
 Resource competition,
 chemical interference, and/or
 parasitism
lead to negative interactions between plants. Root exudates have the
potential to influence all three mechanisms of interference
 For a number of plant species, root exudates play a direct role as
phytotoxins in mediating chemical interference (i.e., allelopathy).
 In addition, root exudates are critical to the development of associations
between some parasitic plants and their hosts.
 root exudates may play important indirect roles in resource competition by
altering soil chemistry, soil processes, and microbial populations.

14.  Positive interactions between plants are also sometimes controlled by root
exudates. In particular, some root exudates induce defense responses in
neighboring plants. In some cases, the plant defenses induced by root
exudates simply reduce susceptibility to pathogen infection, whereas in
other cases these defenses initiate production and release of leafy volatiles
that attract predators of plant enemies. In addition, effects of root exudates
on soil processes and microbial populations can lead to some positive
effects on neighboring plants.

15. Negative Plant-Plant Interactions
• Allelopathy
• Chemical-mediated plant plant interference, or allelopathy, is on
mechanism by which plants may gain an advantage over their
competitors.
• Plants that produce and release potent phytotoxins can reduce the
establishment, growth, or survival of susceptible plant neighbors, thus
reducing competition and increasing resource availability.
 Different phytotoxins in root exudates affect metabolite production,
photosynthesis, respiration, membrane transport, germination, root
growth, shoot growth, and cell mortality in susceptible plants(
Einhellig et .al 1995)

16. Allelopathy

17. Phytotoxins produced by root
 7,8-benzoflavone Acroptilon repens, Russian knapweed (Stermitz et .al
2003)
 catechin (Centaurea maculosa, spotted knapweed) ( Bais et.al 2002)
 DIMBOA and DIBOA (Triticum aestivum, wheat) (Haig et.al 2000 )
 Juglone ( Juglans nigra, black walnut) (Jose et.al 1998)
 sorgoleone (Sorghum spp.) (Nimbal et.al 1996 )
 5,7,4-trihydroxy-3,5-dimethoxyflavone (Oryza sativa, rice) (Kong et.al
2004)
 Phytotoxic root exudates can mediate negative plant-plant interactions only
if presentat sufficient concentrations to affect plant growth and survival.

18. Autotoxicity
• Many plants also produce secondary metabolites that inhibit the
growth of conspecific plants (i.e., autotoxicity). Autotoxicity has been
widely observed in agricultural crops and weeds, as well as in some
plants that inhabit natural systems (Singh et. al 1999).
• In many cases, plants that are allelopathic also exhibit signs of
autotoxicity
• However, only one study has identified that the same root exudate
responsible for both allelopathy and autotoxicity in a plant species.(
Perry et al. 2005) demonstrated that catechin, the phytotoxin
produced by C. maculosa, also inhibits C. maculosa seedling
establishment at high concentrations.

19. Parasitic plant-host interactions
• Root exudates are essential in the development of associations
between parasitic plants and their plant hosts, an association
that is negative for the host and positive for the parasite
• More than 4000 facultative and obligate parasitic plants have
been identified to date (Yoder et. al 1994)
• the role of root exudates in parastic plants has been obtained
from research on Striga asiatica and S. hermonthica (Striga)
infestations of Sorghum Spp .
• Striga have very small seeds that can survive for only a few
days after germination before forming an association with a
host

22. Positive Plant-Plant Interactions
Induced herbivore resistance
 For example, Elytrigia repens (couch-grass) produces several
phytotoxic compounds in its root exudates, of which one,
carboline, has been identified (Glinwood et.al 2003)

23. Induced herbivore defense via predator attraction
• some root exudates induce defense responses in
neighboring plants that reduce herbivore populations
indirectly by attracting predators and parasites of the
offending herbivore.
• For example, V. faba plants under attack release root
exudates that induce green leafy volatile production
in undamaged V. faba plants, which in turn attracts
aphid parasitoids (Dicke et. al 2001)

24. • Similarly, Phaseolus lunatus (lima bean) plants
under attack by spider mites produce root
exudates that induce volatile production in
undamaged P. lunatus plants, attracting
predatory mites( Guerrieri et.al 2002)

26. Mechanisms That Influence Soil Resources
• Some effects of root exudates on both positive and negative plant-plant
interactions may also be mediated by indirect effects on soil resources
(Wardle et. al 1998).
• Root exudation can increase or decrease soil nutrient availability by altering
soil chemistry and soil biological processes.
• Effects of root exudates on soil resource availability may most often be
strongest in the rhizosphere of the plants that produce them, providing a
competitive advantage over neighboring plants that lack the same abilities.
• Here, we discuss two of the mechanisms through which root exudation of
plant secondary metabolites can influence soil resource availability:
phytosiderophore secretion and organic acid
secretion.

27. Phytosiderophores and micronutrient availability
• Some root exudates that act as metal chelators in the rhizosphere
can increase the availability of metallic soil micronutrients,
including iron, manganese, copper, and zinc (Dakora et.al 2002)
• Metal chelators form complexes with soil metals, thus releasing
metals that are bound to soil particles and increasing metal
solubility and mobility.
• The best evidence that plants use chelators in root exudates to
increase micronutrient availability comes from research on the
effects of graminoid phytosiderophores on iron (Fe) availability.

29. • many phenolics produced by dicots
have the potential to form complexes
with metallic micronutrients and may
also increase metal availability

30. Organic acids and phosphorus availability
• Organic acids can also act as metal chelators in the rhizosphere, but are
thought to have more important effects on phosphorus availability than
on micronutrient availability.
• Phosphorus, like iron, is often relatively abundant in soils, but in
unavailable forms. In particular, phosphorus is often bound in insoluble
ferric, aluminum, and calcium phosphates, especially in soils with high
pH.
• Organic acids such as citric, malic, and oxalic acid can form
complexes with the iron or aluminum in ferric and aluminum
phosphates, thus releasing plant-available phosphates into the
soil(Masaoka et.al 1993)

31. PLANT-MICROBE INTERACTIONS MEDIATED BYROOT
EXUDATES
• Plant-microbe interactions can positively influence plant growth
through a variety of mechanisms, including fixation of atmospheric
nitrogen by different classes of proteobacteria (Moulin et .al.,2001).
• Bacteria can also positively interact with plants by producing
protective biofilms or antibiotic operating as biocontrols against
potential pathogens.
• rhizosphere bacteria can also have detrimental effects on plant
health and survival through pathogen or parasite infection.
• Root colonization is important as the first step in infection by soil-
borne pathogens and beneficial associations with microorganisms

32. Positive Plant-Microbe Interactions
 Nodulation of legumes by rhizobia.
 Rhizobia form symbiotic associations with leguminous plants
by fixing atmospheric nitrogen in root nodules.
 Rhizobia legume interactions are very specific, allowing
specific rhizobial strains to nodulate with specific host
legumes.
 Sinorhizobium meliloti effectively nodulates species of the
Medicago,Melilotus, and Trigonella genera, whereas
Rhizobium leguminosarum bv viciae induces nodules in the
Pisum, Vicia, Lens, and Lathyrus genera.

37. Mycorrhizal associations

38. INTRODUCTION
Root – fungus association is called Mycorrhiza.
There are two types of Mycorrhizal fungal association viz.
Ectomycorrhiza and Endomycorrhiza (AM). Mycorrhizal
plants increase the surface area of the root system and
absorb nutrients from soil especially phosphorus and
micronutrients by huphae that goes beyond root zone to
absorb nutrients. Almost 90 % of crop plants are
mycorrhizal mostly of AM type. Therefore, AM association
in crop plants plays significant role in enhancing nutrient
mobilization towards root.

39. Mycorrhiza increase the surface area of the root
Absorb nutrients from soil especially phosphorus
and micronutrients through hyphae and mobilize into
the host cell.
Almost 90 % of crop plants are mycorrhizal mostly of
arbuscular type (AM)
Mycorrhiza possess vesicles and arbuscules.
Mycorrhiza species are: Glomus, Gigaspora,
Scutellospora, Acaulospora, Entrophosphora and
Sclerocystis
CHARACTERISTICS OF ARBUSCULAR MYCORRHIZA

40. Microphotographs of different mycorrhizal type
Hyphal network
Vesicle in root
Ectomycorrhiza
Arbuscule
AM Spores

41. MYCORRHIZA ENHANCES CROP YIELD
Crop
Supplement of P2O5
through VAM (kg/ha)
% Yield increase
over control
Fingermillet 19 18
Soybean 25-50 19
Chillies 37.5 55
Chickpea 40.0 25
Groundnut - 10-20
P supplementation and
mobilization by AM helps
in yield increase
Arbuscular Mycorrhiza (AM) Fungi as component of INM
End Previous Next

42. Benefits of Mycorrhizae
• Increased uptake of nutrients
– Hyphae explore the soil for nutrients, increase surface area for nutrient
absorption transport them back to the plant.
– The nutrients P, Zn, C, N, Cu and S have been shown to be
absorbed and translocated to the host by mycorrhizal fungi
• Increased rootlet size and longevity
– Mycorrhizal plants have larger roots than nonmycorrhizal plants
regardless of whether mycorrhizal fungi are present.

43. • Water relations
– Hyphae explore the soil for water and increase surface area for
absorption
– Some mycorrhizae alter the plant’s physiology, increasing stomatal
resistance, resulting in less water loss.
• Improved growth rate

44. • Increased seedling survival
– Mycorrhiza promotes plant survival, whether new seedlings or out-
planted container stock.
– Survival of inoculated plants can be up to five times the survival of
uninoculated plants.
– Improved survival is no doubt due to a combination of mycorrhizal
benefits, including faster growth to help overtop weeds, protection
from pathogens, and improved drought tolerance.

48. Negative Plant-Microbe Interactions
• Antimicrobial effects
• The role root exudates play in pathogenesis of root-infecting
bacteria and fungi, however, has not been fully appreciated, in part
because of inadequate methods available for analysis.
• Bais et al. 2002, identified rosmarinic acid (RA), a caffeic acid
ester, in the root exudates of hairy root cultures of sweet basil
(Ocimum basilicum) elicited using fungal cell wall extracts from
Phytophthora cinnamoni.
• Basil roots also exuded RA by fungal in situ challenge with
Pythium ultimum, and RA demonstrated potent antimicrobial
activity against an array of soil-borne microorganisms, including
an opportunistic plant pathogen Pseudomonas aeruginosa

49. • Brigham et al. 1999, reported that Lithospermum erythrorhizon
hairy roots showed elicited, cell-specific production of
pigmented naphthoquinones that had biological activity against
soil-borne bacteria and fungi. These findings strongly suggest
the importance of root exudates in defending the rhizosphere
against pathogenic microorganisms.
• concentrations of indolic and phenylpropanoid secondary
metabolites in A. thaliana roots increased upon infection with
the root-pathogenic oomycete Pythium sylvaticum

50. Quorum-sensing inhibitors and signal mimics

57. CONCLUSION
• Understanding of these interactions is incomplete due to the
difficulty of studying underground processes under controlled yet
realistic conditions.
• is now understood that roots are rhizosphere ambassadors
facilitating communication between the plant and other organisms
in the soil.
• identification of the compounds present in the root exudates that
influence the soil microbial community structure and function
would help build novel strategies for improving plant performance
and for increasing crop yield and sustainability

58. Thank
you